A printhead assembly, employed in an inkjet printer, generally includes a heater chip and a flexible circuit being attached on a substrate. A nozzle plate may be disposed on the heater chip. The heater chip may be electrically connected to the flexible circuit through tape automated bonding (TAB) techniques or wire bonding procedures. These electrical connections, which are usually made of metals, should be protected from contact with ink to prevent corrosion. This protection may be provided by encapsulating the electrical connection with corrosion resistant material such as an epoxy-based encapsulant.
To maximize print quality, distance of the nozzle plate of the printhead assembly from the printing media such as paper, which may hereinafter be termed as media gap, should be minimized. But one factor that may limit the reduction of the media gap is the height of the encapsulant that covers the electrical connections of the printhead assembly. Another limiting factor is the cockle phenomenon which occurs when printing media wrinkles or deflects toward the printhead assembly upon depositing the ink. If the combination of the height of the encapsulant measured relative to the surface of the nozzle plate and the cockling height of the printing media exceeds the media gap, the printing media disposed with ink will probably rub on the encapsulant causing the ink to smear across the printing media. The media gap may not be reduced without considering the height of the encapsulant and the effect of cockle phenomenon, thus hindering improvement on print quality.
One known process of encapsulating the electrical connection of the printhead assembly is by dispensing an encapsulant material using a discharge needle. In using this process, the final height of the encapsulant relative to the nozzle plate is typically undesirably high, and encapsulant height variation may be present. Making changes on the dispense process have been so far unsuccessful in providing better control of the encapsulant height. This may be due to the transient properties of the encapsulant material. The properties of the encapsulant material may change with temperature, humidity, and age. The problem may be solved if a more stable encapsulant material which still prevents corrosion is discovered. But to date, encapsulant materials that may be easy to manufacture are not sufficiently corrosion resistant.
Another factor that contributes to the variation of the height of the encapsulant may be the variation of the dispensing volumes of the encapsulant material. Normal tolerances of the components of the dispensing assembly creating the dispensing volume of the encapsulant material may result to the variation of the volume of the encapsulant material being dispensed. So, even with very precise metering and more stable encapsulant materials, height variation may still be at unacceptable levels.
Commonly assigned U.S. Pat. No. 7,121,647 B2 describes another method of encapsulating the electrical connections of the printhead assembly. The encapsulant material is provided on the printhead assembly through stencil printing. This process has the ability to apply more consistent layer of encapsulant at precise locations. But the ability to reduce encapsulant height has not been demonstrated. In this process, the encapsulant material may have the tendency to stick or wick out on the stencil which may possibly result in contamination.
U.S. Pat. No. 7,618,842 B2 illustrates a technique for reducing the height of the encapsulant. A profiling surface such as a blade is used to wipe the top portion of the encapsulant before the encapsulant has cured. The profiling surface moves across the wet encapsulant and displaces the top portion of the encapsulant to the flexible printed circuit board side to flatten the top portion of the encapsulant. This technique may have the tendency to splatter some encapsulant residues on adjacent surfaces of the printhead assembly or stick some encapsulant residues on the profiling surface which may lead to contamination.
Accordingly, a need exists in the art to reduce the height of the encapsulant of the printhead assembly without removing any wet encapsulant or contaminating adjacent surfaces of the printhead assembly. The need extends to reducing media gap and improving print quality. Additional benefits and alternatives are also sought when devising solutions.